Normally we dont openly discuss moderators/duties. (In the rules)
But I do not think they can read PMs. From what I have heard about and received....I think the herd might be thinned quite a bit...but their job is keep us civil openly and only if you file a complaint on a PM is it followed up...but I still don't think they see the actual PM unless someone sends it to them?.
In other forums that use the vBulletin product where I've been a moderator, the answer would be no, the exception being anyone with admin level access to the database itself on the server, which is not typically part of a moderator's volunteer role. Someone has to administer the database, just like the IT techs at a company who hold the keys to the kingdom.
It would be one sorry hacker indeed who wasted time skulking around here lol.
The site team does not have access to any private messages unless they are forwarded to us by the receiver or sender.